Underfeed stoker



C. F. MILLER.

UNDEBVFEED sToKER. I APPLICATION FILED MAY2I, I9I- HIS ATTORNEYS IN FACT.

f5.1.l Mmm.

4 UNDERFEED STOKER.A APPLICATION Af lLED 5MM-21, 1917.

Patented' Feb. 14; 1922.

s SHEETS-SHEET 2.

57 uw la ZI {l/o ATTORNEYS.

C. F. MILLER.

UNDERFEED STOKER. APPLICATION FILI-IU IIIAYZIfIQI.

1,406,883. Patented Feb.14,1922.

g Hls ATTORNEYJI'N FACT discharge mechanism.

, UNITED STATES PATENT I oFricE.

canarias F. MILLER, or PITTSBURGH, rENNsYLvANIA, AssIeNon. To WESTING- IIoUsE ELEcTnIc a MANUFACTURING comm, a CORPORATION. or I'ENNSYI.-

VANIA.

UNDERFEED -sToIrIuik Application med nay 21',

stokers and particularly to stokers operating on 'the underfeed princlple, or those in which fuel is forced into the combustion chamber or furnace below the points at which air or forced draft is supplied, so that some of the volatile constituents of the fuel are distilled oil' and the fuel is partially or wholly converted into coke before mingling with the burning fuel within the combustion chamber.

A n object of the invention is to produce a new and improved underfeed stoker in which improved means are employed for operating the fuel feeding and the refuse discharging mechanism.

A further object is to produce a furnace including new and improved means for feeding fuel into the furnace and for obtaining a substantially uniform fuel surface throughout the furnace area.`

A further object is" to produce means for iznderfeeding fuel into a furnace which dis-v tributes the fuel uniformly over the fuel bed.v support of the furnace and which operates with a minimum amount of resistance.

A further object is to producefa new and improved refuse discharge mechanism and new and improved means for operating the A 'further' obJect. 1s t-o Vproduce an under- `feed furnace in which new and improved means are employed for distributing the airv or forced draft to the fuel bed within the furnace.

These and other objects, which will be .made apparent throughout the further description of the invention are attained b v means of apparatus embodying the features herein. described and illustrated in the draw- -ings accompanying `'and forming .a part hereof.

In the drawings.' Fig. 1 is a longitudinal sectional view of a furnace embodying my invention.

Fig. 2 is a front view of the furnace illustrated in Fig. l.

Specification of Letters Patent.

- plungers or rams the furnace and actuated by which isalso located at the front` 1917. `Serlal R0. 169,932.

Fig. 3 is a fragmental longitudinal sectional view of a furnace and illustrates in' detail the refuse discharge mechanism and the means employed for actuating it.

Fig. 4 illustrates in perspective diferent elements which compose a regulating device for the actuating means of the refuse discharging mechanism; one of the elements is vshown in section for convenience of illustration. i

Fig. 5 is a sectional perspective view of a portionA of theV actuating mechanism of fuel feeding plungerswhich form a part of the stoker illustrated.

Fig. 6 is a perspective end view of the apparatus shown in Fig. 5 and illustrates positions which different parts of the mechanism may assume after a shearing key forming a part of the mechanism, has been sheared by excessive strains on the, mechanism. Y

Fig. 7 is a .perspective view of a form of Patented Feb. 14, 1922'.

shearing key which" may be employed in' connection wlth the apparatus illustrated in Figs. 5 and 6. y

Fig. 8 is a view partially in vertical section and partially in elevation of a portion ofthe actuating means of`the refuse discharge.

mechanism.

The Stoker illustrated as an embodiment of my inventionrincludes an underfeed section shown as a retort 10 which extends across the front of the Stoker and to which fuel is fed at points below the air or blast admission ports or passages, by means of fuel feeding 11 located at the front of a fuel feeding mechanism of the furnace. The fuel after entering the retort 10, is forced onto an over feed section, illustrated as comprising a series of alternately arranged stationary and reciprocating grate bars 12 and 12 which extend from the retort rearwardl to a refuse discharge mechanism 13 locat between the grate bars and the bridge wall 14 of the furnace.

The retort 10 is formed by the cooperation' of so called retort bodies 15, an inclined table 16 and the forward ends of the stationary and reciprocating `grate bars. The bodies l5-are formed in relatively short sections, are'mounted on the inclined table 16, and each includes a fuel hopper 17, located at the front of the furnace, a guide or paS- i sageway in which one of the rams 11 operates, and an air box 18, therear wall of which forms the front wall of the retort 10. The guideway in which the plunger 11 operates is located below the hopper 17 vand forms a means of communication between the hopper and the retort. v v

The inclined table forms in effect the floor of the retort 10 and itsl forward edge is mountedon a box section 19, which extends throughout the width of the furnace and forms the lower portion of the front wall of the Stoker. The rear edge of the inclined table is mounted on a support bar, shown asA an angle bar 20, which extends across the furnace, and is mounted at intermediate points, 011 pedestals 21. The pedestals are shown mounted on frame members 22, which are suitably spaced throughout the width of the furnace and are inl turn mounted on suitable supports such as beams 22a.

The grate bars 12 and 12 are shown inclined downwardly toward the rear of the furnace. Each bar is mounted at its upper end on a support plate or member 21a, which extends from one side-wall to the other of the furnace, and is supported at interme# diate points on the pedestals 21. The lower ends of the grate bars are shbwn supported on a twyer box 24, which extends at right angles to the grate bars and is mounted on theframe members 22. vThe tWyer box is provided in its grate bar supporting face with air delivery ports or passages 24a, which are adapted to communicate with air admission ports formed in lower ends of the hollow bars 12 or 12. l

Air under pressure is delivered to the twyer box 24 through a passage 25, which is formed below the fuel supporting surface of the Stoker by means of plates 26 and 26a livered to each bar is discharged into the chamber 25 througha port or passage 30 formed in the lower face of the bar and 1ocated intermediate its ends. the air -traversing each bar is also discharged into the chamber 25 through ports 31, formed in the bottom face and located immediately adjacent to or near the upper end of the bar. The upper end face of each grate bar is provided with a series of twyer openings or ports 32, which discharge air into the retort 10 substantially at right angles to the Idirection of travel of fuel issu ing from' the retort.

With this arrangement of grate bars the bars :are cooled by the incoming air and the A portion of incoming air is preheated before it is de- 1 livered to the fuel on the 'fuel supportin surfaces. By providing a port 30 in eac grate bar Ireduce the cross-sectional area of the grate bar and at the same time supply enough air through the bars to support combustion within the combustion chamber and vto thoroughly cool the bars. It will, of course, be understood that the rearward portion of`each barl is subjected. to the greatest heat and conse uentl it is desirable to-expose that portion o the bar not only to the coolest air but also to the largest volume of flow of air. With the arran ment illustrated the incoming air is elivered to the lower ends of the grate bars and substantially all of the air entering the furnace traverses the lower ends of the grate bars. The front portions of the grate bars are subjected to less heat, since they are more thoroughly protected by green or )partially burned fuel, and they consequently require less cooling, For thisv reason it is permissible to discharge a portion of the cooling air from the grate bars at intermediate points and thereby render it possible mounted on the frame members 22, and con. to reduce the average COSS-SectiOIl 0f the sequently spaced apart by these members. The upper series of plates 26 divides'the space below the fuel supporting surface oft e stoker into what may be termed the primary air chamber 25 and a secondary airl chamber 25, the latter being located imma. diately below the grate bars 12 and 12 and the inclined table 16. Blast or air under pressure is delivered to the chamber 25 through` a conduit 27 and may be controlled by means of a damper or valve 28 located within the chamber 25 and actuated from the front of the furnace by means of,a rod 29 and a hand wheel 29.

vSubstantially all of the air deliveredto the combustion chamber of the furnace or vStoker irstfpasses through the grate bars 12 and 1 2. Each grate bar is hollow, is provided-on its fuel supporting ,faces with transversely extending serrations located in bars and consequently their Weight.

The preheated air discharged from the ports 30 and 31 is delivered'to the fuel bed through passages formed between the bars 12 and 12', it being understood that the'bars are suitably spaced to permit air to pass lupwardly from the chamber 2 5L into the fuel bed. This preheated air, by being exposed to the heated grate bars, furthercoolsthe barsl and consequently' takes up additional lheat from, the bars as it enters the'coib'ustion chamber. In addition to this, 'thefin-'i clined table 16 is subjected to'the" cooling action of the lair in `the chamber 25"'. The temperature of this airis considerably less lull than the air delivered throug'h theports'l, y

since it has not been subjected `to'theshamel amount of heating., Airis alsodeljvered from the chamber 25 to the'ftw'y'er 18 located in the retort bodies 15. f t

III

y Each retort body contains'a section ofthe Y twyer box and the box extends 'front of the furnace and communicates with the chamber 25a through passages 33, which extend downwardly through the bodies 15 and register With suitably located portsl formed in the inclined table 16. For convenience of manufactureand also for lightl ness of structure, and for the additional purl18, form arches through which fuel is fed by the .rams 11 into the furnace or into the retort 10. The twyer box 18 is provided with a series of .ports 34, which extendl across the front of the furnace and discharge air from the box across the, mouth of the retort, and approximately at an angle to the line of travel of the fuel issuing from the retort. A

As illustrated, the stationary grate bars 12 are held against longitudinal movement by means of lugs 12 and 12b, the former of which engages a rear edge of the plate 21, whereas the latter engages a shoulder formed on the forward edge of the twyer box 24. VV-ith such. an arrangement, the stationary bars are capable of lateral motionl and may be readily removed from the-ir supporting members, but are rmly held against longitudinal motion.

The moving bars are adapted to reciprocate longitudinal-ly and at thev same time tomove in such a Way that their lower ends are periodically projected abovethe plane defined by the fuel supporting surface of the stationary grate-bars. This is accomplis-hed in the Stoker" illustrated by providing the lower ends 'of the bars with supporting faces which are inclined upwardly toward theA rear of the furnace and by forming the grate bar supporting face of the twyer box 24 so that it is inclined at a corresponding angle.

With this arrangement the reciprocating motlonof the grate bars causes theirlower -ends to move upwardly and to attain the highest position when the bars are at the end of their vrearward stroke. As illustrated, the upper 'end of each. bar is "so formed that itsuppersupporting face, which engages the plate 21"` is substantially-horizontal when -the barsare in their normal posit-ions.

The moving grate bars 12 are actuated by means'of a rocker bar 36, which is supported in suitable bearings formed in the pedestals 21 and which .extends from one side to the other of thei furnace. T he rocker'bar iS provided with a downwardly extending arm 37, which is operatively connected by means of a'link 38 and an adjustable lost motion connection to anoscillating lever 39, forming a part of the stroker drive mechanism.

, The lost motion connectionconsists of a rod 40, a fixed collar 40 mounted on the rod and an adjustable collar formed on a sleeve nut 41, which is screwed on to the end of the rod 40%. The fixed collar and the adjustable collar are adapted to engage the arm 39, or a lug provided on it, and to impart motion to the rocker-bar 36.

The stoker drive mechanism illustrated is standardized so that its parts may be duplicated in large stokers. In this connection attention is called to the fact that the retort bodies 15 are standard and interchangeable;

the moving and stationary grate bars 12 and 12 are each of standard construction; and the table 16 and member 19 may be divided into standard lengths, consequently a stoker of substantially any desired width may be built up by assembling the desired number of standard parts.

In v Fig. 2 of the drawings I have illustrated a Stoker of standard width for a boiler of a certain capacity, and it will be seen that this Stoker includes six assembled body portions. In this figure I have illustrated a drive mechanism which will serve the stoker illustrated and which consists of two standard drive mechanisms each adapted to serve that portion of the Stoker includj ing three body portions.

Each standard drive mechanism includes a-shaft 42, which is journaled-in brackets formed on orA secured to the front of .the front wall of-the stoker. The arm 39, whichv imparts oscillatory motion to the'rocker bar 36, is keyed or otherwise rigidly mounted onl the shaft 42.

4The connecting rod 46 is operatively connected to a crank arm 48, whlch is mounted on a crank shaft49. It will be apparent that the crank shaft 49 is adapted to transmit power to each standard drive mechaf n ism and that it is therefore provided with two cranks 48. The shaft 49 may be a continuously rotating shaft and mayr be driven by amotor or engine 50.

The fuell rams 11 are periodicallyvreciprocated bythe shafts 42, it being understood that l'each shaft 42 of the Stoker illustrated in- Fig.;'2 operates three fuel rams. The operative connection between each ram 11 and its operating shaft 42 is such that it may be broken without injury to the ram, the driving mechanism, or any, of the- Stoker' parts, in case the ram encounters. abnormal resistance tomotion. In the apparatus illustrated this is accomplished by providing a two-part gear hereinafter more fully describedv which is mounted on the operatin l shaft 42 and. meshes with a rack 11, form 0n theram 11. The two parts of the gear are adapted to be secured together by what may be termed a shearing key, which is of sufficient strength to transmit normal strains, but is so designed that it will shear when subjected to abnormal strains, and thereby release the rack engaging portion of the gear from the driving shaft 42.

In Figs. 5 and 6, I have illustrated the two part gear employed for driving one of the rams 11. Each gear consists of an inner or hub portion 51, which may be keyed or otherwise rigidly mounted on the shaft 42, and an outer or rack engaging portion 52, which surrounds the hub portion 51 and is adapted to be rigidly 'locked to it by means of a shearing key 53. It will, of course, be understood that for convenience of assembling, the outer portions 52 may, and preferably will be formed in semi-annular segments, as illustrated in Figs. 5 and 6, and that one segment only need be provided with gear teeth, for engaging rack 11. The number of teeth on the toothed segment will depend upon the desired throw of the ram 11, and the angle of oscillation of the shaft 42, and thediameter of the segment. It will also be understood that any desired means may be employed for preventing lateral motion of the outer portion of the gear, with relation to the hub portion, after the shearing key has been severed byundue strain. I have. illustrated the hub portion 51 as provided with a key seat 54 which may be of hardened or specially tempered -metal and which is adapted to receive the shearing key 53. The portion 52 is als provided with a key seat or way which operates with the seat 54 in receiving the key The key, as illustrated in Fig. 7. is bifurcated at the end adapted to project beyond the key ways and is so arranged that a projecting tip 53 is formed on each portion of the severed key by means of which the separate portions may be removed from the ways. This arrangement of two part gear and shearing key is an improvement over similar devices adapted to fail and to thereby prevent the parts from being subject to breaking strains,

' since the strains imparted to the shearing keydo not vary for different positions of the gear, consequently an abnormal resist.-

l ance `to motion, encountered by the ram. at

1 any point .in its stroke will shear'the pin,

and the position of the pin is not a determining factor in the amount of stress to which it is subjected.

--The shafts 42 also actuate the refuse discharge mechanism 13. Asillustrated, the mechanism' 13 includes two dump grate mechanisms. each actuated by one of the shafts 42 and serving one half thewstoker, or a portionfmadeup' ofthr'ee retort bodies 15 'and cooperating grate bars 12 and 12 ram l1, etopEa'ch dump mechanism illustrated is of thiJ type known as the double leaf dump and includes two tilting dump grates 55 and 56. The grate 55 is located immediately adjacent to the lower' ends of the inclined grate bars and so arranged that its rear edge is adapted to move downwardly when the grate is tilted for the purpose of dumping refuse into the ash pit. Each rear tilting grate 56 is'mounted adjacent to the bridge wall 14, so that its forward edge moves downwardly when the grate is tilted for the purpose of dis- .charging into the ash pit.. With this arrangement the grates 55 and 56 cooperate in bridging the space between the grate bars 12, 12 and the bridge wall. As illustrated, each of the dump grates 55 and-56 is so formed that they cooperate to produce a crushing action kon the clinker or othei` material supported on them as they are moved to the dumping position. This is accomplished by pivoting each grate at a point intermediate its forward and rear edges so that one edge will move upwardly and inwardly an appreciable distance as the'other edge moves downwardly and outwardly to accomplish the dumping. Referring to the grate 55, it will be seen` that it is pivoted at a point intermediate its forward and rear edges but that the trunnion about which it turnsis located nearer the forward edge than the rear edge. The forward edge is also provided with an upwardly projecting jaw 5i'` which extends 'transversely of the furnace and which cooperates with a similar jaw 5S formed on the grate 56 in crushing the material located on or above the dump grates at the time of dumping.

In Fig. 3, I have illustrated one dump Grate mechanism in section and moved to the cumping osition, whereas the other dump grate mec anism, serving the farther half of the Stoker, is shown-so far as possible-in elevation and is the normal or closed position. In order to prevent the dump grate #from burning out and also to prevent the burning ofll of the crushing jaws 5T and 58, each dump grate is hollow or is provided with cooling passages through which air may be circulated while-the grates are in the closed position. As illustrated, each dump grate is provided with a passage 59 which extends from the jaw edge of the grate substantially to its downwardly moving edge, and air is delivered to this passage through a port 60 which registers with ai port 61vwhen the grateA is in a closed position. The passages 59 are both open so that ash or solid material will be discharged from them either bythe force of the blast passing through them,l or by gravity when the grates are moved to the dumping position. The port 61, adapted to supply'air to the .grate 55, is located in therrear wall of the air box 24, whereas the port 61 supplyingair to the opconti positely disposed grate 56 is located in the Vforward wall of an air box 62, which is mounted on or is built into the bridge wall 14.

In order to prevent the unnecessary discharge of air from the ports 61, during the dumping period, but primarily to prevent the ash or solid material :from falling into the space between each grate and the adjacent air boX during the dumping period, each D which is adaptedto close the port 61 and prevent the passage of ash or solid material between the grate and the-adj acent air box. As illustrated', each apron 63 is located along the jaw edge of the grate and the apron and the ous face of the jaw is curved, the center o curvature being at the pivot point of the grate. With such an arrangement each apron forms a valve for the port 61 and a gate to prevent ash from lodging in behind the ate. For the purpose of burning out all t e carbon contained in the ash support-` ed on the grates prior to dumping, I have provided a port in the air passage 25 for the purpose of delivering blast to the ash pitorv the dump grates. This valve 26", which is in' to the space below port is controlled by a turn controlled by a rod 26 which projects through the front of the furnace.

The grates 55 and 56 are operated by the Each pair of grates is operatively shaft 42. connected to its operating shaft by means of a lever 64 rigidly mounted on the shaft, an

' adjustable lost motion connection 65, a bell the shaft 73, av

'Parting crank 66, a rack 67, a ar 68 meshing with the rack, and a dumping lever and crank, which are actuated by the gear 68. T he bell crank 66 is pivotally mounted 'on a bracket at the front of the furnace and transmits mov tion to the rack 67 by means of a link 69 and a rod 70, the rod rejecting through the front of the furnace. ll)`he rack 67 is located below the dump grates but out of the Vline of discharge intothe ash pit. The rear grate 56 is actuated by means of a lever 71 and a link 72. The lever 71 is illustrated as being keyed on a'shat 7 3 on which the gear 68 1s mounted, and the link 72 is pivotallyfconnected to an arm 74, which may be mount ed on or otherwise rigidly secured to; the grate 56. The forward grate is operated by a correspondmg arrangement of and levers including the lever 75,l mounted on link 76 and a lever 77. The' levers 71 and 7 5 are 'so mounted on the shaft 73thata oftheg'earGSwillsimultaneously moveA th rates 55 and 56.v In Fig. 1, the gratos are the corresponding position of the rack, the gear and the levers 71- and 75 are clearly illustrated. In moving the tes to "the dummgnpoltion, the rack 67 1s moved toward t e of the furnace, thereby ima and simultaneously moving both the levers 71? rate is provided with a depending apron 63 a clockwise motion to the gear 68 and 75 in a clockwise direction. In Fig. 3 the actuating membersof the grates shown in section are .indicated by reference numerals, whereas the actuating members of the other dump grate mechanism are unnumbered; this is done for the purpose of avoiding confusion, and for indicating the positions assumed by the levers 71 and 75 when the gratas are fully open.

'The lost mot'on connection 65 includes oppositely threaded screws 80 and 81, which are rigidly mounted on ahub portion. The hub is provided with an operating hand wheel 83 and also with a cylindrical guide and abutment portion 84which surrounds the screws 80 and 8l. A sleeve nut 85 is threaded on to the screw 80 and a -sleeve 85"L is threaded on to the screw 81. These sleeve nuts telescope with the cylindrical guide 84 and are adapted to be moved to different longitudinal positions, relatively to the guide, by a turning of the hub. A combination trunnion and block 86 is slidably mounted on the sleeve nut 85 and is adapted to form the operative connection between' the adjustable connection member and the lever64. For this reason it is provided with a trunnion 86a which is journaled in a boss formed on the outer end of the lever 64. The

longi udinal motion of the block 86 along the sleeve 85 is limited by the upper end of the member 84 and a collar formed on the upper end of the sleeve 85. The sleeve 85 is prevented from turning about the screw 80 by the cooperation of a set screw 87 mounted on the block A86 and a slot 88 formed in the sleeve 85. The adjustable connection 65 crank 66 by means of a combination trunnion and block 8,6, ed on the sleeve nut 85". Turning the hand :wheel 83' in one direction moves both the slee've nuts outwardly and thereb;l increases the free motion of both of the blocks 86 and 86 along their mounting sleeve nuts. A turning of the hand wheel in the other direction decreases the free motion of the blocks 86 `and 86 and when the sleeves 85 and 85* reach their innermost position, with relation to the member 84, the blocks 86. and 86 are locked against relative longitudinal motion and the entire motion of the lever 64 is imparted to the bell crank 66.

With this arrangement the dum grates may be moved romthe closed to t e fully open ition, or they may be moved from they c osed to any intermediate position. When it is desired to retain thegrates in the closed sition, the hand wheel 83 is turned so t at no opening motion will be imparted bythe adjustable connection 65 to a bell crank 66. In 1, I have shown the member-84-with the sleeve nuts extended to such positions. that no motion is imparted to the dump gratos. In Fig. 3, the adjustwhich is slidably mount` Jable connection 65 is shown adjusted to not swing from the closed to the dumping position, I have substantially balanced each grate about its trunnion, and in addition to this,-I have so arranged the links cooperating with the levers 71 and 75 that there is no tendency for unbalanced forces to swing the grates from the fully closed to the fully open position. By a reference to Fig. 1, 1t will be apparent that the levers 71 and 75 are so positioned that each is substantially at dead center, so far as the connecting links are concerned, when the grates are in the fully closed position and consequently neither grate can impart a turning movement to the gear 68, but it must remain locked in the closed position untilthe rack is shifted through the agency of theconnecting device 65. Y

i The operation of the stoker illustrated is asfollows: The shaft 49 is driven at a relatively slow, speed; the oscillations of the shafts 42 connected thereto are therefore relatively slow, resulting in an appreciable interval of time for each oscillation. The

' cranks 48 are 'so positioned on the shaft 49 that one shaft 42, of the Stoker illustrated, is moving through the fuel'feeding portion `of its -strokewhile the other shaft 42 is withdrawing the fuel Elungers The shaft 49 is consequently su jected to continual resistance, since one shaft 42 takes up the load occasionedv by forcing fuel into 4the furnace as soon as the other is relieved' of this load; The 'rams force lfuel from' the permanent one and if employed will accom' hoppers into the retort 10 and, after the re-l tort is full, the fuel is crowded out of the retort on to the grate bars 12 and 12. The inclination of` the/grate bars and the reciprocaton ofthe moving bars `12" cause the fuel to movedownwardly across the bars and to be eventually deposited on the dump grates. The reciprocatlon of the grate bars 12 not only augments the downward travel of thefuel, but tends to break up the fuel bed and to maintain a substantially constant distribution of the fuel over the 4fuel supportingsurfaces.u As previously stated, the connection 'may beadjusted to impart a full opening and closing motiorLto the dump grates or it may-be adjusted to impart an lntermediate o ning motion to the grates. This latter adjustment' may be a relatively plish a continuous l.discharge of ash from the furnace. Under ordinary operatingon'- ditions the dump gratcs will be opened periodically, remaining full closed .between dumping periods. The umping operation will then consist in the connection 65, as illustrated in Fig.

pleted one cycle in which it has moved the gratos yfrom the closed to the fullyopen and then back to the closed position. After thls is accomplished the adjustment of the corr-Y nection will be changed to that illustrated 1n Fig. 1, and the shaft 42 willV then impart no motion to the grates or their operating mechanisms.

All the air entering the combustion chamber of the Stoker is first delivered-to the primary air chamber 25. The inlet port to this chamber is controlled by the valve 28, and the valve may be adjusted to meet the desired conditions of blast., The air periodically delivered to the ashpit and through the valve 26" is not materially preheated be# fore entering the fuel bed, but with this exception all air entering the fuel bed is first employed in cooling a fuel supporti member and consequently is preheated. T e preheatin is advantageous for two reasons: first t e air delivered to the green fuel as it leaves the retort 10 should be hot enough to aid in the distillation of the fuel and second, the more exposed parts o f'the furnace should be more efectually cooled than parts protected by an adequate bed of green or fresh fuel. The air delivered tothe twyer openings along the sides of the retort 1s therefore subjected to .maximum heating, whereas the large volume of air delivered to other portions of the fuel bed is subjected to o -less preheating in order that it may be more ports '31, whereas the remainder ofthe air passing through the grate bars is delivered to the chamber 25.V A portion ofthisair is delivered directly to `the fuel bed between the ates 12 and 12', and the remainder is furtler heated in its passage to the twyer box 18 and is delivered to the twyers 34.-

In Fi 1, I have shown air delivery ports 71* in -t e front wall of the stoker for delivering the preheated air to the combustion chamber above the fuel bed. These ports receive air from the air box 72,

through a port which may be controlled from the front of the furnace by a valve 73".

While I have described but one embodiment of. my invention, it will be apparent thatV various changes, modifications,b additions,gomissions and substitutions may be A made in` the apparatus illustrated without departing from the'spirit and scope of the invention, as set forth by the appended A claims. u 3, and maintaining th1s adjustment until ,the arm 75 has com- What I claim is: Y p 1. In combination in a Stoker, a fuel'feed mechanism, a retort extending across the lao alternate stationary and. movable grate bars 1,4oe,esa

front of the Stoker, alternate movable and stationary grate bars inclined rearwardly from the retort, .a d'scharge mechanism at the rear of the grate bars, means for actuating the fuel feed mechanism, the movable grate bars and the discharge mechanism uniformly, and means included in the actuating means forimparting a variable relative mo-l tion to thedischarge mechanism.

2. In combination in a stoker, a retort extending across the front of the stoker,

having their forward ends supported by the bottom of the retort and arrangedto form a wall of said retort and said bars extending downwardly toward the rear of the furnace, fuel feeding rams spaced along the retort and so located that fuel is fed into the retort below the surface of the fuel maintained therein, a dump grate mechanism located adjacent .to the lower edge of the grate bars, a driving mechanismfor actuating said rams, dump grate mechanism, and means carried by fthe drive mechanism for imparting yan adjustable range of motion to 'the dump grate mechanism during the normal operation of the rams and grate bars.

3. 'In combination in a Stoker,- a retort extending across the front of the stoker, a series of hollow grate bars extending substantially at right angles to said retort, receiving the fuel discharged therefrom,

and having air ports for delivering air'into j the fuel issuing from 'the retort, a tuyere box having a ported wall on which the -fuel of said grate bars are slidably mounted, ports in the bearing surfaces of the discharge ends of said bars registering with the ports in said ported wall to deliver' air to the hollow interior of said bars, a primary a 1r chamber communicating .with and dehver'lng air to 'sald tuyere box, a seconda air chamber locatedimmediately below sai grate bars and` said retort and to which air is.delivered from saidv grate bars,

and means for delivering air from Said secondary 4chamber to' said fuel issuing from said retorts.

`4. In combinationl in a Stoker, a retort, a plurality of grate bars extending substantially at right angles to said retort, their adjacent ends forming awall of the retort, a tuyere box slidably supporting the far ends of said bars,.each grate prising a hollow member having air delivery mary air chamber located below the` grate' bars of said Stoker and commumcatmg. with ports formed in the retort end thereof, an air admission portformed in the opposite a cooperat- 1n portion of said tuyere box, and an air delivery port formed in the lower faceof the the bar, a primovable grate bars and the and the 'delivery ports bar comsaid tuyere box, and a secondary air chamber located between the primary air chamber and the grate bars and immediately below air acrossv the mouth of theV retort, means adjacent the rear ends of the bars for delivering air to the discharge 'mechanism,y air.delivery ports located intermediate the ends of said bars, and means for delivering major portion of the air entering the combustion chamber of the furnace through the hollow grate bars.

6. In a forced draft Stoker, an underfeed section, an overfeed section, an air admitting dump grate, and a tuyere box supporting the overfeed section and adapted to supply air to said overfeed section and dump grate, the overfeed section comprising a plurality of hollow grate bars, sald bars adapted to receive air from the tuyere box and deliver the same to the underfeed and overfeed sections.

7. The combination with a Stoker having a primary air chamber at the discharge end of the grate, a dump grate chamber at the rear of the I )riniarychamber, a secondary chamber communicatin with the fire box, of a. grate having a p bars, each'bar having an air admission port communicating with the primary chamber, a

delivery port at the center o-f each bar opening into the secondary chamber, and a' hollow.'dump grate having air admission ports communicating Awiththe primary chamber 8'. The combination having a tuyere box at the discharge end of the grate and an air chamber beneath the grate, of a grate having a plurality of hol# low-grate'bars,`each bar having ran admis'- air chamber, each bar being reduced in crow-sectionalfarea along said delivery ports. Y

, 9. A Stoker comprising 'a interchangeable retort bodies provided with. fueladmission-. aages andconstituting a front wall of urality of hollow grate -105 along the upperside in fa stoker furnace retort forma by sion port communicating with the tuyere 'box' and deliveryv ports along the bar open-A -ing into the said 12 t e retort, a series of grate bars for'receiving vfuel from the retort, the Q sides of the barsv constituting a rear wall .of

bodies and said bars are mounted, and means the retort, aninclined table upon which said 10. A'mechanical Stoker for comv grate bars, each having one rend mounted upon said table, the ends ofthe bars cooper` ating with said bodies and with said table to form a retort extending acro the front of the furnace, said bars extending from the A retort toward the rear of the furnace, means tween said hub and Said toothed member,

for forcing fuel through the fuel' admission passages and means located at the front of the furnace for 'actuating said fuel feeding means.

11. Incombination with the fuel feeding mechanism of a Stoker, a drive shaft, a two -part gear mounted on saidshaft and comprising a hub portion rigidly mounted on the shaft and a toothed member rotatably mounted on said shaft, a shearing key beand an operative connection between said toothed member and said fuel feeding mechanism. l

12. In combination in a, progressive feed Stoker, av retort, a plurality of inclined hollow reciprocating grate bars provided with inlet passages and arranged to receive fuel from the retort, a twyerbox supporting the lower ends of the grate bars, air passages in the twyer box cooperating with said inlet passages in the rate bars, respectively, and a plurality of elivery lopeningsl along the bottom of each bar, the flowarea within each bar being successively decreased in cross-sectional area between the delivery openings from the first to the last of said openings,

In testimony whereof, I have hereunto subscribed my name this 19th day of May, 1917.

CHARLES F. MILLER. 

